Carbon Quantum Dot/Chitosan‐Derived Hydrogels with Photo‐stress‐pH Multiresponsiveness for Wearable Sensors

Abstract

In recent years, hydrogels have attracted extensive attention in smart sensing owing to their biocompatibility and high elasticity. However, it is still a challenge to develop hydrogels with excellent multiple responsiveness for smart wearable sensors. In this paper, a facile synthesis of carbon quantum dots (CQDs)-doped cross-linked chitosan quaternary/carboxymethylcellulose hydrogels (CCCDs) is presented. Designing of dual network hydrogels decorated with CQDs provides abundant crosslinking and improves the mechanical properties of the hydrogels. The hydrogel-based strain sensor exhibits excellent sensitivity (gauge factor: 9.88), linearity (R 2 : 0.97), stretchable ability (stress: 0.67 MPa; strain: 404%), good cyclicity, and durability. The luminescent properties are endowed by the CQDs further broaden the application of hydrogels for realizing flexible electronics. More interestingly, the strain sensor based on CCCDs hydrogel demonstrates photo responsiveness (𝚫R/R 0 ≈20%) and pH responsiveness (pH range ≈4-7) performance. CCCDs hydrogels can be used for gesture recognition and light sensing switch. As a proof-of-concept, a smart wearable sensor is designed for monitoring human activities and detecting pH variation in human sweat during exercise. This study reveals new possibilities for further applications in wearable health monitoring.

Ultrafast Self‐Healing, Superstretchable, and Ultra‐Strong Polymer Cluster‐Based Adhesive Based on Aromatic Acid Cross‐Linkers for Excellent Hydrogel Strain Sensors

“…The pH value of the PAA‐ co ‐PAAS@ohPEI@TTpy hydrogel was ≈5.28, similar to the acidity of human skin. [ 58 ] It did not cause any discomfort such as allergies even after 24 h of contact. Figure a shows the regular resistance changes along with the repetitive finger bending in the durability experiment of the hydrogel sensor.…”

Recent Advances in Wearable Sensors for the Monitoring of Sweat: A Comprehensive Tendency Summary

“…Doping CQDs can be made into pH-sensitive sensing materials. Wei et al [104] obtained a good pH response (4~7) by using N-doped CQDs (yellow fluorescence) and hydrogel impregnation doping, and a proof of concept was performed for sweat detection during exercise. In addition, biomass-derived CQDs can be extracted from natural wood fibers, which reduces environmental pollution during production and still achieves excellent fluorescence performance [105].…”

Photo‐Controllable Smart Hydrogels for Biomedical Application: A Review

“…With its outstanding mechanical qualities and responsiveness, the produced dual-network hydrogel based on CQDs was better suited for use in wearable smart sensors. [263] Ionic conductive hydrogels may first provide a visible photosensitive response in all types of traditional conductive materials due to their great transparency, which is a quick and efficient way compared to other complex photosensitive materials. [264,265] However, due to the intrinsic stiffness of conductive polymer conjugated structures and the incompatibility of conductive fillers with hydrogel substrates, it is difficult to create robust, self-healing, and conductive hydrogels.…”

“…With its outstanding mechanical qualities and responsiveness, the produced dual‐network hydrogel based on CQDs was better suited for use in wearable smart sensors. [ 263 ]…”